1. Field of the Invention
The present invention relates to a permanent magnet type synchronous motor used as a super high-speed variable speed motor for driving a compressor or the like, and also relates to a compressor using thereof.
2. Related Art
Permanent magnet type synchronous motors have been prosperously used for industrial drive sources since its motor efficiency is high. If the rotational speed of the motor is low, permanent magnets are directly bonded to the shaft thereof, but the permanent magnets would be fragmented and scattered if the rotational speed of the motor is high.
As measures for eliminating the above-mentioned disadvantages, there has been provided a super-high speed permanent magnet type synchronous motor, in which carbon fibers or titanium rings are used surrounding around permanent magnets, as disclosed in Japanese Laid-Open Patent No. H10-243586 (prior art 1).
Further, a rotor structure used in a high speed generator is composed of a nonmagnetic porous cylindrical member formed therein with air pores and formed around the outer periphery of a shaft, a laminated electromagnetic steel sheet, segmented magnets, and a reinforcing member made of carbon fibers or the like, which are stacked one upon another in the mentioned order, around the shaft, is disclosed in Japanese Laid-Open Patent No. H10-248186 (prior art 2).
In the above-mentioned prior art 1, although the permanent magnets can be prevented from being fragmented and scattered, but no consideration has not yet been made for a problem of loss caused in the rotor when the permanent magnet type synchronous motor is driven by an inverter so as to cause pulsating magnetic flux, due to harmonic current, to be induced in the rotor.
In the above-mentioned prior art 2, the permanent magnets are thermally demagnetized due to a copper loss or an iron loss of the generator, and accordingly, a rotor structure for cooling the rotor itself with air has been proposed in order to prevent thermal demagnetization of the rotor. However, since the output power of the generator rotated at a high speed, inevitably has a high frequency, no consideration is made for a loss induced in the rotor when pulsating magnetic flux caused by high frequency current is induced in the rotor in such a case that an inverter for converting high frequency power into a power having 50 Hz or 60 Hz is added. Further, it has been arranged in such a way that the main magnetic flux of the permanent magnets is led through the laminated electromagnetic steel sheets, and no consideration has not yet been made to such a problem that the allowable speed is restrained by the mechanical strength of the laminated electromagnetic steel sheets themselves.
The present invention is devised in view of the above-mentioned points, and accordingly, an object of the present invention is to provide a permanent magnet type synchronous motor in which less loss is induced in a rotor even though it is driven by an inverter which is operated at a basic frequency of around 1 kHz, and an air compressor using the magnetic type synchronous motor.
To the end according to the present invention, there is provided a permanent type synchronous motor is composed of a stator in which armature windings are wound in a plurality of slots in a stator core, conductive permanent magnets which are provided around the outer periphery of a magnetic shaft, and a rotor provided therearound with a reinforcing member made of carbon fibers, wherein a laminated electromagnet steel sheet is interposed between the shaft and the permanent magnets, and the laminated electromagnetic steel sheet is a high tensile strength electromagnetic steel sheet, and further, there is provided an air compressor using the permanent type synchronous motor.
The magnetic flux from the permanent magnets is led to the stator through the laminated electromagnetic steel sheet and the shaft of the rotor. Further, when the permanent magnet type motor is driven by an inverter having a basic frequency of around 1 kHz, harmonic magnetic flux is induced, being caused by harmonic current from the inverter. This harmonic wave has a frequency which is 5, 7, 11, 13, 17 or 19 times as high as the basic frequency, and accordingly, harmonic loss would be caused in several components. The largest harmonic loss is induced from the shaft with no laminated electromagnetic steel sheet, which would be as high as several kW, and accordingly, a super-high speed permanent magnetic type synchronous motor is not available. However, with the provision of the laminated electromagnetic steel sheet between the shaft and the permanent magnets, as in the present invention, since the harmonic magnetic flux passes through the laminated electromagnetic steel sheet, bypassing the shaft, no shaft loss is caused, and accordingly, the loss can be decreased down to several hundreds W corresponding to iron loss of the laminated electromagnetic steel sheet.
Further, a permanent magnet type synchronous motor having a peripheral speed of a rotor as high as several hundreds m/s, for directly driving an air compressor would cause such a disadvantage that a laminated electromagnet steel sheet provided in the rotor would be deformed by elongation due to centrifugal force. On the contrary according to the present invention, the high tension type electromagnetic steel sheet is desirably used in the rotor. For example, an electromagnetic steel sheet having a tensile strength of 70 kg/mm2 is used, no deformation of the laminated electromagnetic steel plate due to elongation is caused, and accordingly, there can be provided a super-high speed permanent magnet type synchronous motor and an air compressor using thereof.